A conventional lock includes a housing, a central cylinder and a plurality of tumbler members. The central cylinder is inserted into the housing, is rotatable relative to the housing, and has a straight keyway that is formed through an insertion end thereof. Each of the tumbler members is mounted movably between the housing and the central cylinder, extends into the keyway, and is operable to move between a holding position, where the tumbler member is inserted into both of the housing and the central cylinder to prevent the relative rotation between the housing and the central cylinder, and a released position, where the tumbler member is retracted into one of the housing and the central cylinder to permit the relative rotation between the housing and the central cylinder.
Each of the tumbler members can be accessed by a straight key blade that is inserted into the keyway, so as to be driven to move to the released position to permit the relative rotation between the housing and the central cylinder. However, the conventional lock is easily picked since a picking tool may be easily inserted into the straight keyway to access the tumbler members.